Two Days Before 2nd Half

With record temperatures forecast for today, tomorrow, and possibly race day, I am growing concerned that heat, not just hills, will be a factor during my second half marathon. Even though I am running today's 3 mile orbit during race hours, I can already feel the heat even though clouds are still reducing the direct impact of the sun's rays. Fortunately, it is not stopping me from hitting my pace target, but I am not sure how far into the morning I would be able to maintain this if it gets much hotter.